The plaintiffs argue it's not free speech if their speech is so far away it can't be heard.

Massachusetts set up a 35-foot buffer zone around Planned Parenthood clinics that offer abortions.

Supporters say it's about public safety. Two abortion clinic workers were killed there in 1994. "We see a lot of protesters actually threatening intimidating doctors, women, administrative staff as they are trying to get in the building," said the President of NARAL Pro-Choice America Ilyse Hogue.

The buffer zone, they argue, is no different than restricting campaigning near places where people vote. "It's not that their messages can't be seen and heard but what it does do is protect the women and the administrative staff and doctors from that kind of in your face harassment that is really damaging," said Hogue

But the Supreme Court will hear today from plaintiffs who argue the law targets only one kind of speech - people who oppose abortion.

That, they say, is unconstitutional. "What Massachusetts is doing here is picking sides in one of the most divisive issues in our country today].] They are saying the abortion clinics reps are free to speak but the sidewalk counselors are not," said Carrie Severino, Judicial Crisis Network.

The court upheld a similar Colorado law 13 years ago. There's also a law creating abortion protest zones in Montana.

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